Fume hood

ABSTRACT

A fume hood is provided with an auxiliary air flow assembly which, when the sash is up, divides the incoming auxiliary air into a portion which flows directly into the work enclosure of the hood and a portion which flows downwardly and outwardly from the hood into the room to be drawn into the work enclosure. A diffuser and a directional air grille are positioned below the auxiliary air inlet between the sash and the front panel of the hood, and a dividing plate extends generally vertically upwardly from the air grille forwardly of the sash. Auxiliary air flows generally vertically downwardly through the diffuser toward the air grille. The divider plate directs a portion of this downwardly flowing air between the divider plate and the sash where it is drawn into the work enclosure, and the remainder of the auxiliary air flows through the air grille. The air grille includes directional vanes which directs the air outwardly and downwardly from the upper portion of the work opening to be drawn into the work enclosure across the work surface.

United States Patent [1 1 Turko et al.

[451 July 24,1973

[ FUME HOOD [73] Assignee: American Hospital Supply Corporation, Evanston, Ill.

[22] Filed: Aug. 18, 1971 [21] Appl. No.: 172,746

[52] U.S. Cl. 98/115 LH [51] Int. Cl. F23j 11/00 [58] Field of Search 98/115 LH, 36;

Primary ExaminerWilliam F. ODea Assistant Examiner-Paul Devinsky Attorney-Dawson, Tilton, Fallon 8L Lungmus [57] ABSTRACT A fume hood is provided with an auxiliary air flow assembly which, when the sash is up, divides the incoming auxiliary air into a portion which flows directly into the work enclosure of the hood and a portion which flows downwardly and outwardly from the hood into the room to be drawn into the work enclosure. A diffuser and a directional air grille are positioned below the auxiliary air inlet between the sash and the front panel of the hood, and a dividing plate extends generally vertically upwardly from the air grille forwardly of the sash. Auxiliary air flows generally vertically downwardly through the diffuser toward the air grille. The divider plate directs a portion of this downwardly flowing air between the divider plate and the sash where it is drawn into the work enclosure, and the remainder of the auxiliary air flows through the air grille. The air grille includes directional vanes which directs the air outwardly and downwardly from the upper portion of the work opening to be drawn into the work enclosure across the work surface.

9 Claims, 11 Drawing Figures PAIENTED JUL24I975 sum 1 [if 3 INVEN'JORS: MICHAEL TURKO g LYNN LSEYMOUR amfiaug y, (fa 44 ai 1% FUME noon BACKGROUND This invention relates to fume hoods, and, more particularly, to a fume hood which is provided with an improved auxiliary air flow system.

Fume hoods are commonly used in the laboratory for providing a ventilated work area for laboratory activities involving hazardous materials, generated fumes, aerosols, gases and particulate matter. The fume hood protects laboratory personnel and equipment by confining, containing and exhausting these materials.

Fume hood systems conventionally include an exhaust blower for removing air from the fume hood, and when fume hoods are installed in air conditioned laboratories, they withdraw cooled or conditioned air from the laboratory. Since the conditioned air has been supplied to the laboratory at substantial expense, it is desirable to reduce the amount of this costly air which is withdrawn from the laboratory.

Balanced air fume hoods are designed to reduce the amount of conditioned air which is consumed by supplying untempered, non-conditioned air, or auxiliary air, to the fume hood. The auxiliary air is introduced into the hood, and it is important that some of the auxiliary air and any conditioned air which is drawn into the fume hood from the laboratory sweep across the entire work surface to prevent the escape of fumes from the hood. Also, it is desirable to draw as much as possible of the auxiliary air to the exhaust system so that untempered air does not mix with or dilute the room air and thereby interfere with the attempt to provide a comfortable work environment.

SUMMARY The invention provides a balanced air fume hood with an auxiliary air flow assembly which directs a substantially uniform flow of air through the work enclosure. When the sash is opened, auxiliary air flows downwardly through the auxiliary air chamber, and a divider plate directs a portion of this air directly into the work enclosure. The remainder of the auxiliary air passes through a directional grille which guides the air downwardly and outwardly from the work opening. This auxiliary air together with captured room air is then drawn through the lower portion of the work opening by the exhaust blower and is swept across the work surface. The volume of auxiliary air is not sufficient to satisfy. the exhaust, and about 25 percent of the air exhausted is drawn from the laboratory. The resulting inward flow of air from the laboratory through the fume hood substantially prevents the escape of any fumes through the work opening. When the sash is closed, the auxiliary air flows over the divider plate into the work enclosure where it is exhausted. Laboratory air is drawn into the work enclosure through the directional air grille and the foil to satisfy the exhaust requirements, thereby preventing the escape of fumes. Fume hoods made in accordance with the invention enjoy very little loss of auxiliary air, substantially eliminate counterflows within the hood, and effectively exhaust the entire hooded area.

DESCRIPTION OF THE DRAWING The invention will be explained in conjunction with an illustrative embodiment shown in the accompanying drawing, in which FIG. 1 is a perspective view of a balanced air fume hood constructed in accordance with the invention;

FIG. 2 is a front elevational view, partially broken away, of the fume hood of FIG. I;

FIG. 3 is an enlarged fragmentary sectional view taken along the line 3-3 of FIG. 2;

FIG. 4 is an enlarged fragmentary view of a portion of the air grille;

FIG. 5 is a top plan view of the air grille taken along line 55 of FIG. 4;

FIG. 6 is an enlarged fragmentary view of a portion of the directional air grille;

FIG. 7 is a fragmentary top plan view of the air diffuser;

FIG. 8 is a fragmentary sectional view of the air diffuser taken along line 8--8 of FIG. 7;

FIG. 9 is a schematic sectional view of the fume hood illustrating the air flow when the sash is open;

FIG. 10 is a schematic view similar to FIG. 9 illustrating the air flow when the sash is closed; and

FIG. 11 is a fragmentary sectional view taken along the line 1111 of FIG. 2.

DESCRIPTION OF SPECIFIC EMBODIMENT Referring to FIGS. l-3, the numeral 15 designates generally a balanced air fume hood having a frame 16 which includes a base 17, a counter top 18 which provides a working surface, and a superstructure 19 mounted on the counter top.

The superstructure 19 includes spaced-apart side walls or panels 20 and 21, rear wall or panel 22, and top wall or panel 23. The walls 20-23 are generally orthogonally related and, together with the counter top or bottom wall 18 define a work enclosure 25. An auxiliary air chamber designated generally by the numeral 24 extends between the side walls 20 and 21 and terminates above the counter top 18 to provide an access opening 26 to the work enclosure, and the opening can be closed by a sash 27 which is slidable vertically in tracks 28 secured to the side walls: behind the auxiliary air chamber. The sash is shown in its lower position in FIGS. 2 and 3, and in a partially raised position in FIG. 1. The sash may advantageously include a glass window to permit observation of materials withinthe work enclosure when the sash is closed.

An exhaust opening 30 is provided through the rear portion of the top wall 23, and an exhaust collar 31 is secured to the top wall above the opening and is adapted to be connected to a conventional exhaust air blower (not shown). A light opening 32 may also be provided through the top wall, and a light 33 may be mounted above the light opening.

A baffle assembly 34 is mounted within the working enclosure adjacent the rear wall for providing desired directional flow through the work enclosure under the influence of the exhaust blower. The baffle assembly extends between the two side walls and includes angularly related upper baffle plates 35 and 36 joined by bracket 37 and a lower baffle plate 38. The upper baffle plates 35 and 36 are supported by elongated rods 40 which extends into the bracket 37 and are supported by a pair of supports 41 secured to the side wall. The lower baffle plate 38 is supported by a pair of supporting blocks 42 adjacent the side panels, and the spacing of the baffle plate 38 from the rear wall can be adjusted by the adjusting block 43. The lower end of the baffle plate 36 is spaced from the baffle plate 38 by a plurality of spaced-apart spacers 44 secured to the baffle plate 38.

As can be seen best in FIG. 3, a foil 45 extends between the side walls at the front of the working enclosure and includes an upwardly and rearwardly inclined front portion 45a and a generally horizontally extending portion 45b which is spaced above the countertop 18 to provide an air passage 46 between the foil and the working surface of the countertop.

Referring to FIGS. 2, 3 and 11, the integral auxiliary air inlet chamber 24 is formed by a front panel 47, rear panel 48, side panels 49 and 50, and top panel 51. The side walls and 21 are each seen to be provided by a pair of spaced-apart panels 20a and 20b and 21a and 21b, respectively, and the sides 49 and 50 extend inwardly adjacent the inner wall panels 20b and 21b. The front panel 47 extends laterally outwardly to the outer wall panels 20a and 21a and terminates in a pair of rearwardly extending flange portions 47a which extend adjacent the wall panels 20b and 21b. The air chamber may be removably attached to the side walls by means of screws or the like.

An inlet opening 52 is provided through the top panel 51, and an air inlet collar 53 is mounted above the inlet air opening and adapted to be connected to a conventional air blower.

The rear panel 48 is substantially shorter than the front panel 47 and terminates in a forwardly extending support flange 54 (FIG. 3) which supports a pair of forwardly extending support ledges 55 and 56. A support bracket 57 is secured to the front panel and supports a pair of rearwardly extending support ledges 58 and 59. A generally planar air diffuser 60 is supported by the ledges 56 and 59, and a generally planar air grille 61 is supported by the ledges 55 and 58. The diffuser 60 and air grille 61 extend between the side panels 49 and 50 so that substantially all of the incoming auxiliary air flows therethrough.

Referring now to FIGS. 4 and 5, the particular air grille 61 illustrated is formed from an expanded metal sheet having a plurality of rows of openings 62 and a plurality of elongated metal strips 63. The strips 63 are intermittently separated and expanded to form the openings in the conventional manner, but the strips are twisted approximately 45 from the plane of the sheet to form inclined side surfaces 64 which extend at an angle of about 45 with respect to the plane of the sheet. The openings 62 are somewhat elliptical, with the long dimensions of the openings extending laterally between the side panels of the fume hood, and the openings of each row are staggered relative to the openings of the adjacent rows. In the illustration given the air grille 61 is positioned so that the strips or vanes 63 are inclined downwardly and rearwardly, but the air grille can be positioned so that these vanes extend downwardly and rearwardly if desired.

Referring to FIGS. 7 and 8, the air diffuser 60 is advantageously formed of a plurality of thin sheets 65 of expanded metal to provide several mesh-like layers of metal with the openings of each layer randomly superposed over the openings of the layer therebelow. The layers are pressed together, and the random arrangement of the openings provides a circuitous path for the air flowing therethrough.

Another directional air grille 66 is supported adjacent the bottom of the front panel 47 by an angularly downwardly and rearwardly extending bottom panel 67 (FIGS. 3 and 11) which is provided with a central rectangular opening 68 and which terminates in an upwardly extending rear flange 69. The grille 66 covers the opening 68 and is formed from an expanded metal sheet in the same manner as the grille 61. The grille 66 is positioned so that the directional vanes 70 (FIG. 6) thereof are inclined downwardly and outwardly and is supported by the panel 67 in an inclined position from the horizontal. The angle of inclination of the plane of the grille from the horizontal is advantageously about 20 to about 25, and the directional air vanes thereof are arranged to guide air outwardly and downwardly at an angle of approximately 45 from the horizontal.

A solid air dividing plate 73 is secured to the flange 69 and extends vertically upwardly therefrom between the side panels. The dividing plate is generally aligned with the rear edge of the upper air grille 61 and is spaced forwardly of the sash 27 to provide an air flow passage 74 therebetween.

The fume hood may also include conventional nozzles 75 for gas, water, and the like, which are operated by the control valves 76.

The operation of the fume hood will be explained with reference to FIGS. 9 and 10. FIG. 9 illustrates the operation of hood when the sash 27 is raised, as when work is being performed on materials within the work enclosure. Air within the work enclosure is exhausted through the exhaust collar 31 by the exhaust air blower, and the arrows illustrate the exhaust flow of the air around the baffle plate into the exhaust plenum which is defined by the baffle plates and the upper right corner of the superstructure. The air is drawn through the space between the bottom of baffle plate 38 and the work surface, through the space between the baffle plates 36 and 38, and through the space between the upper end of the baffle plate 35 and the top panel 23. The baffle plates ensure that the air being exhausted sweeps across substantially the entire working enclosure.

Auxiliary air is supplied through the inlet air collar 53 by the auxiliary air blower, and the auxiliary air passes downwardly through the air diffuser 60 and the air grille 61. The air diffuser creates a back pressure on the incoming auxiliary air and ensures that the air passing through the diffuser and the grille 61 is of substantially uniform velocity throughout the length of the inlet air chamber from one side panel to the other. The auxiliary air flows generally vertically downwardly within the inlet air chamber between the front panel 47 and the sash until the air reaches the air dividing plate 73, which permits a portion of the air to flow downwardly along the sash between the sash and the dividing plate and directly into the work enclosure as indicated by the arrows 78. The remainder of the auxiliary air passes downwardly through the directional air grille 66 which guides it forwardly and downwardly, and a portion of this auxiliary air, indicated by the arrows 79, flows into the laboratory and combines with room air, indicated by arrows 80. As this auxiliary air continues to flow downwardly, it is drawn inwardly by the exhaust blower through the lower portion of the work opening and sweeps across the top of the foil 45 and the work surface. Room air is also drawn into the work enclosure with this auxiliary air to help satisfy the exhaust requirements of the blower, and additional room air, indicated by the arrow 81, is drawn into the fume hood through the air passage 46 between the foil and the work surface. Some of the auxiliary air, indicated by the arrows d2, does not escape the work enclosure and is drawn through the central portion of the work opening. A generally uniform flow of air is thereby provided through the entire work opening, and the escape of fumes from the hood is substantially prevented.

The auxiliary air blower supplies about 75 percent of the air necessary to satisfy the exhaust air blower, and the remaining 25 percent is drawn from the room air. The flow of air from the room into the hood also ensures against the escape of fumes, and, since substantially all of the auxiliary air is captured by the exhaust, very little, if any, auxiliary air passes outwardly of the foil 45. Downward air flow outwardly of the foil is undesirable since this may draw air from within the hood through the flow passage d6 between the foil and work surface.

Referring to FIG. llti), when the sash is closed the auxiliary air is allowed to flow directly from the air grille 61 into the work enclosure above the air dividing plate 73 as indicated by the arrows b3. Since the auxiliary air is insufficient to satisfy all of the exhaust requirements, substantially all of the auxiliary air flows directly from the inlet air chamber into the work enclosure, and the remaining air necessary to satisfy the exhaust require ment flows from the room into the work enclosure through the grille 6b and through the space between the dividing plate and the sash is illustrated by the arrows 84 and 85, respectively, and through the space between the foil and the working surface as indicated by the arrow db. The air is directed around and between the baffle plates as hereinbefore described relative to FIG. 9 and is exhausted through the exhaust collar 351i.

From the foregoing, it will be seen that a constant flow of air is provided over the working surface whether the sash is open, closed, or partially open, and since there is a constant inflow of air throughout the entire fume hood opening, there is little likelihood that fumes will escape from the hood.

While in the foregoing specification, a detailed description of a specific embodiment of the invention was set forth for the purpose of illustration, it is to be understood that many of the details herein given may be varied considerably by those skilled in the art without departing from the spirit and scope of the invention.

We claim: a

l. in a fume hood having a frame including front, rear, side, top and bottom panel means defining a work enclosure, the front panel means terminating above the bottom panel means to provide a front opening, a generally vertically extending sash slidably mounted between the side panel means and being slidable vertically between a lowered position in which it covers the front opening and a raised position, auxiliary air inlet means, and air exhaust means, an improved auxiliary air flow assembly comprising panel means secured to the frame below the auxiliary air inlet means to provide an auxiliary air inlet chamber communicating with the work enclosure, a directional air grille mounted in the auxiliary air inlet chamber adjacent the bottom thereof for directing auxiliary air downwardly and forwardly from the auxiliary air inlet chamber, an air dividing plate extending upwardly adjacent the rear of the directional air grille and spaced forwardly of the sash, auxiliary air flowing downwardly through the air inlet chamber being divided by the air dividing plate when the sash is in the lowered position into a first portion which flows through the directional air grille and a second portion which flows between the air dividing plate and the sash and into the work enclosure, auxiliary air flowing directly into the work enclosure from the air inlet chamber above the air dividing plate when the sash is in the raised position.

2. The structure of claim l in which the directional air grille is positioned adjacent the lower end of the front panel means whereby auxiliary air is directed forwardly from the work enclosure at the upper portion of the front opening.

3. The structure of claim t in which the air grille is positioned adjacent the lower end of the front panel means and includes vane means for directing auxiliary air downwardly and forwardly at the upper portion of the front opening at an angle of approximately 45 from the horizontal.

d. The structure of claim 3 in which the air grille is generally planar and extends upwardly and forwardly from the air dividing plate to the front panel at an angle with respect to the horizontal, the vane means being inclined with respect to the plane of the grille by about 45.

5. The structure of claim 4 in which the air grille is inclined at an angle of about 20 to about 25 from the horizontal.

6. A fume hood comprising a frame including top, rear, and side panels and awork surface defining a work enclosure, a generally vertically extending sash extending between the side panels and being mounted for vertical sliding movement between raised and lowered positions, a generally vertically extending front panel secured to the frame forwardly of the sash, the bottom of the front panel being spaced above the work surface to provide an access opening between the front panel and the work surface, a generally vertically extending air dividing plate extending between the side panels and spaced forwardly of the sash, the top of the air dividing plate terminating below the top panel and the bottom of the air dividing plate terminating above the work surface, a directional air grille extending between the side panels and extending generally forwardly from the air dividing plate to the front panel, the

air grille including vane means for directing air passing generally downwardly therethrough downwardly and forwardly from the bottom of the front panel, auxiliary air inlet means for supplying auxiliary air. to the fume hood above the air grille, and exhaust means for withdrawing air from the work enclosure whereby when the sash is in a raised position auxiliary air flows downwardly between the sash and the front panel and a portion of the auxiliary air flows between the air dividing plate and the sash into the work enclosure and a portion of the auxiliary air flows between the front'panel and the air dividing plate through the directional air griile.

I. The structure of claim ti in which the bottom of the air dividing plate terminates slightly below the bottom of the front panel, the directional air grille extending at an angle from the horizontal from adjacent the bottom of the air dividing plate to adjacent the bottom of the front panel.

3. The structure of claim 6 in which the directional air grille is formed from a generallly planar metal sheet which is provided with a plurality of rows of spaced openings, the portions of the sheet between the openings being inclined from the plane of the sheet whereby panel terminating above the air dividing plate, and an air diffuser extending between the downwardly extending panel and the front panel whereby auxiliary air supplied by the auxiliary air inlet means flows through the air diffuser to provide the auxiliary air with substantially uniform velocity.

* i t i @ERTEFICATE OF CORRECTEON Patent No. 3,747,504 Dated Julv 24 1973 Q Inven Michae] Turko and Lynn L. Sevmour 1 2; is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the last hne of col umn 5, change lowered" to -ra1sed-- and in the sixth hne of column 6, change "raised" to -1owered--.

0 g; and said this fif Day Of August 1975 [SEAL] Arrest:

' RUTHVC. mesow c. MARSHALL DANN Allfl'mg Office ('nmmissinncr uflau'ms and Trademarks 

1. In a fume hood having a frame including front, rear, side, top and bottom panel means defining a work enclosure, the front panel means terminating above the bottom panel means to provide a front opening, a generally vertically extending sash slidably mounted between the side panel means and being slidable vertically between a lowered position in which it covers the front opening and a raised position, auxiliary air inlet means, and air exhaust means, an improved auxiliary air flow assembly comprising panel means secured to the frame below the auxiliary air inlet means to provide an auxiliary air inlet chamber communicating with the work enclosure, a directional air grille mounted in the auxiliary air inlet chamber adjacent the bottom thereof for directing auxiliary air downwardly and forwardly from the auxiliary air inlet chamber, an air dividing plate extending upwardly adjacent the rear of the directional air grille and spaced forwardly of the sash, auxiliary air flowing downwardly through the air inlet chamber being divided by the air dividing plate when the sash is in the lowered position into a first portion which flows through the directional air grille and a second portion which flows between the air dividing plate and the sash and into the work enclosure, auxiliary air flowing directly into the work enclosure from the air inlet chamber above the air dividing plate when the sash is in the raised position.
 2. The structure of claim 1 in which the directional air grille is positioned adjacent the lower end of the front panel means whereby auxiliary air is directed forwardly from the work enclosure at the upper portion of the front opening.
 3. The structure of claim 1 in which the air grille is positioned adjacent the lower end of the front panel means and includes vane means for directing auxiliary air downwardly and forwardly at the upper portion of the front opening at an angle of approximately 45* from the horizontal.
 4. The structure of claim 3 in which the air grille is generally planar and extends upwardly and forwardly from the air dividing plate to the front panel at an angle with respect to the horizontal, the vane means being inclined with respect to the plane of the grille by about 45*.
 5. The structurE of claim 4 in which the air grille is inclined at an angle of about 20* to about 25* from the horizontal.
 6. A fume hood comprising a frame including top, rear, and side panels and a work surface defining a work enclosure, a generally vertically extending sash extending between the side panels and being mounted for vertical sliding movement between raised and lowered positions, a generally vertically extending front panel secured to the frame forwardly of the sash, the bottom of the front panel being spaced above the work surface to provide an access opening between the front panel and the work surface, a generally vertically extending air dividing plate extending between the side panels and spaced forwardly of the sash, the top of the air dividing plate terminating below the top panel and the bottom of the air dividing plate terminating above the work surface, a directional air grille extending between the side panels and extending generally forwardly from the air dividing plate to the front panel, the air grille including vane means for directing air passing generally downwardly therethrough downwardly and forwardly from the bottom of the front panel, auxiliary air inlet means for supplying auxiliary air to the fume hood above the air grille, and exhaust means for withdrawing air from the work enclosure whereby when the sash is in a raised position auxiliary air flows downwardly between the sash and the front panel and a portion of the auxiliary air flows between the air dividing plate and the sash into the work enclosure and a portion of the auxiliary air flows between the front panel and the air dividing plate through the directional air grille.
 7. The structure of claim 6 in which the bottom of the air dividing plate terminates slightly below the bottom of the front panel, the directional air grille extending at an angle from the horizontal from adjacent the bottom of the air dividing plate to adjacent the bottom of the front panel.
 8. The structure of claim 6 in which the directional air grille is formed from a generally planar metal sheet which is provided with a plurality of rows of spaced openings, the portions of the sheet between the openings being inclined from the plane of the sheet whereby air flowing through the opening is directed at an acute angle with respect to the plane of the grille.
 9. The structure of claim 6 including a panel extending downwardly from the top panel between the side panels and spaced forwardly of the sash to provide an air inlet chamber between the front, side and downwardly extending panels, the downwardly extending panel terminating above the air dividing plate, and an air diffuser extending between the downwardly extending panel and the front panel whereby auxiliary air supplied by the auxiliary air inlet means flows through the air diffuser to provide the auxiliary air with substantially uniform velocity. 